Anisotropic magnetoresistance in Co2(Fe,Mn)Si Heusler epitaxial films: A fingerprint of half-metallicity

Abstract

The anisotropic magnetoresistance (AMR) effect was systematically investigated in epitaxially grown Co${}_{2}$Fe${}_{x}$Mn${}_{1\ensuremath{-}x}$Si films against Fe composition $x$ and the annealing temperature. A change of sign in the AMR ratio from negative to positive was clearly detected when $x$ increased from 0.6 to 0.8. This sign reversal can reasonably be explained by the change in the dominant $s$-$d$ scattering process from $s\ensuremath{\uparrow}\ensuremath{\rightarrow}d\ensuremath{\uparrow}$ to $s\ensuremath{\uparrow}\ensuremath{\rightarrow}d\ensuremath{\downarrow}$ caused by the creation of large $d$-states at the Fermi level, suggesting the disappearance of half-metallicity at $x$ $=$ 0.8. The variations in the remanent density of states in the half-metallic gap against annealing temperature are also discussed from the viewpoint of the AMR ratio on the basis of the $s$-$d$ scattering model.